The present invention is generally directed to toner processes, and more specifically, to aggregation and coalescence processes for the preparation of toner compositions In embodiments, the present invention is directed to the economical in situ chemical preparation of toners without the utilization of the known pulverization and/or classification methods, and wherein in embodiments toner compositions with an average volume diameter of from about 1 to about 25, and preferably from 1 to about 10 microns, and narrow GSD of, for example, from about 1.2 to about 1.4, and from about 1.16 to about 1.35 as measured on the Coulter Counter can be obtained. The resulting toners can be selected for known electrophotographic imaging and printing processes, including color processes, and lithography In embodiments, the present invention is directed to a process for the preparation of toner, or toner particles comprised of resin and pigment, and wherein a cationic resin emulsion is selected, and wherein cationic based initiators and surfactants are selected. The emulsion particles are preferably adjusted to a high pH of, for example, from about 10 to about 12 by adding a base component thereto, followed by aggregation with pigments and anionic surfactant adjusted to a particle size ranging from about 4 to about 11 microns with a geometric distribution of from about 1.2 to about 1.4 by the addition of cationic surfactant, and heated to enable coalescing of the resin and pigment, and which heating is accomplished at an effective temperature of, for example, from about 50 to about 95.degree. C. Of importance with respect to the processes of the present invention is preparing, or providing a cationic emulsion resin latex comprised of at least one olefinic nonpolar monomer, a cationic olefinic monomer, a cationic free radical initiator, and optionally a chain transfer agent in an aqueous mixture comprised of a nonionic surfactant and a cationic surfactant. A number of advantages are associated with the processes of the present invention including enabling the generation of positively charging stable toners, such as from about 5 to about 30 microcoulombs per gram as measured by the Faraday Triboelectric Cage
There is illustrated in U.S. Pat. No. 4,996,127 a toner of associated particles of secondary particles comprising primary particles of a polymer having acidic or basic polar groups and a coloring agent. The polymers selected for the toners of the '127 patent can be prepared by an emulsion polymerization method, see for example columns 4 and 5 of this patent. In column 7 of this '127 patent, it is indicated that the toner can be prepared by mixing the required amount of coloring agent and optional charge additive with an emulsion of the polymer having an acidic or basic polar group obtained by emulsion polymerization. Also, see column 9, lines 50 to 55, wherein a polar monomer, such as acrylic acid, in the emulsion resin is necessary, and toner preparation is not obtained without the use, for example, of acrylic acid polar group, see Comparative Example I. In U.S. Pat. No. 4,983,488, there is disclosed a process for the preparation of toners by the polymerization of a polymerizable monomer dispersed by emulsification in the presence of a colorant and/or a magnetic powder to prepare a principal resin component, and then effecting coagulation of the resulting polymerization liquid in such a manner that the particles in the liquid after coagulation have diameters suitable for a toner. It is indicated in column 9 of this patent that coagulated particles of 1 to 100, and particularly 3 to 70, are obtained. Negatively charged rather than positively charged toners are believed to be obtained with these prior art processes in that, for example, anionically generated toner particles result.
Emulsion/aggregation processes, especially anionic processes for the preparation of toners, are illustrated in a number of Xerox patents, the disclosures of which are totally incorporated herein by reference, such as U.S. Pat. No. 5,290,654, U.S. Pat. No. 5,278,020, U.S. Pat. No. 5,308,734, U.S. Pat. No. 5,346,797, U.S. Pat. No. 5,370,963, U.S. Pat. No. 5,344,738, U.S. Pat. No. 5,403,693, U.S. Pat. No. 5,418,108, U.S. Pat. No. 5,364,729, and U.S. Pat. No. 5,346,797.
In a number of prior art patents, the emulsion-aggregation process is primarily directed to anionic latexes and anionic initiators in acidic pH to enable the preparation of negative charging toners. With the present invention, positive charging toners are prepared by an emulsion aggregation process involving cationic latexes, and more importantly utilizing cationic initiators, and wherein the process is accomplished in basic pH range of greater than 7 and preferably from about 10 to about 12.
In the present invention, a process for the preparation of a positively charging toner is illustrated, and which process includes in embodiments a number of steps, of which one is comprised of generating a cationic resin latex derived from at least one olefinic monomer such as styrene, butyl acrylate, butadiene and the like, a cationic monomer such as vinylpyridine, acrylamide, 3-methacryloxy-2-hydroxypropyltrimethyl ammonium chloride salt and the like, a cationic free radical initiator such as 2,2'-azobis(N,N'-dimethylene isobutyramidine) dihydrochloride and the like, a nonionic surfactant and cationic surfactant. Another step involves adjusting the cationic latex to a pH of from about 8 to about 14, and preferably of from about 10 to about 12 utilizing a base such as an alkali hydroxide, or an alkali metal carbonate, such as sodium hydroxide or sodium carbonate, and followed by adding a pigment dispersion with an anionic surfactant thereby resulting in a composite aggregate comprised of cationic emulsion particles and pigment, wherein the composite particle has a particle size of from about 5 to about 9 microns (volume average diameter throughout) and a geometric size distribution of from about 1.2 to about 1.4. Subsequently, the composite resulting is heated to a temperature above the glass transition temperature of the latex to afford coalesced toner particles, followed by filtration, washing, and drying to yield positive charging toners.
It is believed that the triboelectric charge of a toner is influenced not only by the pigments and additives selected, but also by the composition of the resin. Generally, anionic groups on the resin such as carboxylic acid and its alkali derivatives, sulfonic acid groups or its alkali derivatives provide negative charging toners. Additionally, when initiators are used in preparing the resin, such as by emulsion process, for example, potassium persulfate or ammonium persulfate, this results in further addition of moieties on the resin and contribute to the charging of the resultant toner. Thus, anionic initiators, such as potassium persulfate or ammonium persulfate, contribute to the negative charging of toners. In contrast, cationic groups on a resin, such as nitrogen containing groups, for example pyridine moieties, tetralkyl ammonium salts or phosphines, result in positively charging toners. Similarly, when the resin is prepared by an emulsion process, cationic initiators are preferred such as the hydrochloride salts of azo bisamidines and the like.